1. Field of the Art
This invention relates to a method and an apparatus for treating surfaces of substrates such as of LCD panels, semiconductor wafers, magnetic storage disks and optical storage disks which are formed of glass, semiconductor, synthetic resin, ceramics, metals or a composite material of these materials, and more particularly to a method and an apparatus for treating substrate surfaces by irradiation of ultraviolet light in a washing or etching stage of a fabrication process.
2. Prior Art
For instance, a circuit pattern including transparent electrodes is formed on a TFT substrate which constitutes a transparent substrate of an LCD panel by the use of a film-forming means. In suc a substrate fabrication process, surfaces of substrates are processed by washing and etching treatments. In a processing of this sort, it has been the general practice to employ a wet process in which treating liquids are applied or injected on substrate surfaces. However, recently the so-call dry processes are introduced into this field, carrying out washing and etching treatments by irradiation of ultraviolet light.
For example, Japanese Laid-Open Patent Application H5-224167 discloses a method of washing glass substrates of LCD panel. In this case, substrates are irradiated with ultraviolet light prior to starting a wet process using a washing liquid. In this known washing method, substrate surfaces are irradiated with ultraviolet light from a low-pressure mercury lamp in a preparatory stage leading to a washing stage. By irradiation of ultraviolet light, organic substances on the substrate surfaces are chemically removed, and at the same time wettability of substrate surfaces is improved to have a smaller contact angle for removing inorganic contaminants efficiently when subsequently washed in a shower or the like. In this regard, ultraviolet light from a low-pressure mercury lamp has peaks approximately at 185 nm and 254 nm in wavelength distribution. Ultraviolet light with such wavelength distribution characteristics can remove organic substances which have deposited on substrate surfaces.
The mechanism of washing off organic substances by ultraviolet irradiation includes decomposition of organic substances into products of low molecular weights by severing chemical bonds, and activation of decomposed products. In addition, simultaneously ozone is produced as a result of absorption of ultraviolet light by oxygen in the air, and ozone is converted into active oxygen. Therefore, through oxidative destructive reactions with active oxygen, activated organic contaminants are finally converted into volatile substances such as COx, H2O, NOx are released into the air, that is, removed from substrate surfaces.
As mentioned hereinbefore, ultraviolet light which is irradiated from a low-pressure mercury lamp has a wavelength of 185 nm on the shorter side. Therefore, of various organic compounds which have deposited on substrate surfaces, the ultraviolet light may not be able to decompose those compounds which have chemical bonds of strong energy like double bonds. This means that ultraviolet light of shorter wavelengths should be employed, in order to wash substrates more completely.
In an attempt to solve this problem, proposed in Japanese Laid-Open Patent Specification H7-196303 is a method of dry-washing work, irradiating substrate surfaces with vacuum ultraviolet light from a dielectric barrier discharge lamp.
In the case of this washing method according to Japanese Laid-Open Patent Specification H7-196303, in removing organic contaminants which have deposited on substrate surfaces, active oxidative decomposition products are produced by chemical reaction with ultraviolet light rays in vacuum. Namely, in this case, ultraviolet light rays of 172 nm which are irradiated from a dielectric barrier discharge lamp decompose organic substances into products of low molecular weight by destructing chemical bonds in the organic substances, while at the same time activating the decomposition products. At the same time, oxygen in the air is decomposed and activated by the action of the ultraviolet light. Therefore, the activated organic substances are converted into volatile substances such as COx, H2O, NOx and so forth by oxidative reactions with active oxygen and ultimately released into the air. As a result, the treated substrate surfaces come to have a smaller contact angle in terms of wettability.
However, since ultraviolet light is consumed for cracking oxygen in the air, an air layer between the discharge lamp and a substrate is increased in thickness to cause an exponential attenuation to the amount of ultraviolet light rays which can reach a substrate surface. Consequently, there occur conspicuous degradations in the capacities of activating organic substances on substrate surfaces and producing active oxygen in the vicinity of substrate surfaces, that is, in the capacity of removing contaminant organic substances by ultraviolet light. Besides, it is only active oxidative decomposition products that are produced by irradiation of an oxygen-containing fluid with ultraviolet light in vacuum. Therefore, depending upon the kinds of organic substances which have deposited on substrate surfaces, it is often found difficult to remove deposited organic contaminants from substrate surfaces simply by oxidative reactions.
In view of the foregoing situations, it is an object of the present invention to enhance the accuracy and efficiency in washing or treating substrate surfaces with ultraviolet light rays. It is a more specific object of the present invention to enhance decomposing effects on organic contaminant substances on substrate surfaces while at the same time minimizing the contact angle of substrate surfaces by irradiating same with ultraviolet light in an atmosphere substantially free of oxygen.
It is another object of the present invention to provide a method and an apparatus for producing an oxidative active member and a reducing active member by irradiating substrate surfaces with ultraviolet light rays in a mixed atmosphere of an inert gas and, thereby ensuring reactions with decomposition products of organic substances to proceed efficiently in an assured manner.
In accordance with the present invention, for achieving the above-stated objectives, there is provided an apparatus for treating substrate surfaces, which comprises: a lamp house located over a substrate transfer path and face to face with a treating surface of a substrate being transferred along the transfer path by a conveyer means; a dielectric barrier discharge lamp fixedly mounted in the lamp house to irradiate ultravilot light toward the substrate; and a moistened inert gas generating means adapted to supply a water vaporcontaining moistened inert gas to a space between the substrate and the dielectric barrier discharge lamp; producing a reducing active member [H.] and an oxidative active member [.OH] by irradiating said moistened inert gas with ultraviolet light from said dielectric barrier discharge lamp.
The lamp house may be arranged to have an ultraviolet light transmitting window on the side which faces a substrate under treatment. Alternatively, in a case where the lamp house is provided within a chamber, it may be opened to the chamber on the side which faces a substrate. In such a case, an inert gas feed means is connected to the lamp house to put the latter in an inert gas atmosphere. The chamber is put in a moistened inert gas atmosphere which is substantially free of oxygen, between entrance and exit openings which are provided at upstream and downstream ends for substrates to be treated. Alternatively, the lamp house may left open on the side of the chamber, or may be fitted with such a partition member on the open side as will transmit ultraviolet light and contain a large number of passages to let the inert gas flow out.
In another form of the present invention, the lamp house is located in and opened to the chamber, and an inert gas feed means is connected to the lamp house. Further, the moistened inert gas generating means may be arranged to include a moistened inert gas feed means which is connected to the chamber to supply a water vapor-containing moistened inert gas toward the surface of a substrate.
Alternatively, the moistened inert gas generating means may be constituted by a pure water vessel which is located within the chamber with an upper open end face to face with the lamp house across the substrate transfer path, and an inert gas feed means which is provided with blow holes to blow an inert gas into the pure water vessel.
On the other hand, according to the present invention, there is also provided a method for treating substrate surfaces, which comprises the steps of: placing a substrate in a mixed atmosphere of an inert gas and water vapor under irradiation of ultraviolet light from a dielectric barrier discharge lamp, thereby splitting water vapor into a reducing active member [H.] and an oxidative active member [.OH]; and letting the reducing and oxidative active members [H.] and [.OH] contact with a surface of said substrate to be treated.
According to a more specific form of the present invention, the method for treating substrate surfaces comprises the steps of: horizontally transferring a substrate into a mixed atmosphere of an inert gas and water vapor under irradiation of ultraviolet light from a dielectric barrier discharge lamp, thereby decomposing organic substances deposited on a surface of the substrate and at the same time splitting water vapor into a reducing active member [H.] and an oxidative active member [.OH]; dry-washing and minimizing contact angle of a surface of the substrate by subjecting the reducing and oxidative active members [H.] and [.OH] to reactions with decomposition products of the organic substances; wet-washing the substrate by supplying a wash liquid thereto; and drying the substrate.
The above and other objects, features and advantages of the present invention will become apparent from the following particular description of the invention, taken in conjunction with the accompanying drawings. Needless to say, the accompanying drawings show by way of example some preferred embodiments of the present invention for illustrative purposes only, and should not be construed as being limitative of the invention in any way whatsoever.